Doğa Gülhan & İnci Ayhan
Apparent duration can be manipulated in a local region of visual field by long-term adaptation to motion or flicker (Johnston et al., 2006). These effects show narrow spatial tuning (Ayhan et al., 2009), as well as retinotopic position dependency (Bruno et al., 2010), supporting early locus in the visual pathway. Here we introduce a novel effect, where a rather short-term adaptor (RDK pattern, 700ms, 2.5°/s or 9°/s) induced a significant subjective duration compression (~10%) on a subsequently presented test stimulus (RDK pattern, 2.5°/s or 9°/s) only for global motion patterns drifting at 50% motion coherence but not for those at 0% coherence, suggesting a higher-level area as a source of origin. In order to investigate the direction specifity, we conducted another experiment using plaids as adaptor (600ms, 2.5°/s) and gratings as tests. In blocked trials of 2-AFC tasks using method of constants, participants compared the duration of a comparison grating (300-1200ms, 2.5°/s drift) to the duration of a standard grating (600ms, 2.5°/s drift) following adaptation. A significant duration compression was only visible when the plaid adaptor and the upcoming standard test moved in the same direction. Direction specific adaptation effects being non-significant for plaid’s component directions indicate a locus where global motion is processed. Further experiments showed that the duration effects cannot be explained by adaptation-induced changes in perceived speed, perceived onset-and-offset and attentional resource allocation, implying separate mechanisms mediating duration effects in higher-level motion areas.